This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Mycobacterium tuberculosis is a highly successful human pathogen that has evolved to survive within the host. Our long-term goals are to delineate the mechanisms by which M. tuberculosis interferes with the microbicidal functions of macrophages and evades host immune responses. Understanding the molecular mechanisms underlying M. tuberculosis-host interactions is important for designing therapeutic interventions and vaccine strategies. We have identified Rv2224c, a predicted protease, as being critical for survival in macrophages and in vivo. We hypothesize that Rv2224c is an important virulence factor that proteolytically cleaves M. tuberculosis substrates and modulates the host immune response. While proteases are known to be key virulence factors in other bacterial pathogens, the function of proteases in M. tuberculosis pathogenesis has been largely unexplored. Our preliminary studies indicate that Rv2224c is exported to the cell envelope of mycobacteria. A mutant disrupted in the protease is impaired for growth in macrophages and in vivo. Mice infected with a protease mutant show markedly reduced lung pathology and survive longer than wildtype-infected mice and we have new evidence that Rv2224c modulates host innate immunity. UPDATE 2010 We have demonstrated that Rv2224c suppresses innate immune responses;Rv2224c mutants induce enhanced proinflammatory responses downstream of Toll-like receptor 2 (TLR2)-signaling in macrophages. We have delineated the host pathways that are involved in suppression.